Efficient, Stable, and Scalable Push–Pull Heptamethines for Electro-Optics

Abstract

Currently, there is increasing interest in the use of push–pull heptamethine chromophores containing the 2-dicyanomethylidene-3-cyano-4,5,5-trimethyl-2,5-dihydrofuran (TCF) electron acceptor for electro-optic (EO) applications. Compared with the benchmark push–pull tetraenes with a stronger trifluoromethyl-substituted TCF acceptor (CF3-TCF), the TCF-based push–pull heptamethines showed lower EO activities; however, they have better chemical and thermal stability and higher synthetic efficacy. Herein we report the facile synthesis and analysis of structure–property relationship of dipolar heptamethines containing a strong electron acceptor, bis­(4-fluorophenyl)-substituted TCF (FP-TCF). The FP-TCF acceptor was synthesized through two consecutive multiple steps, one-pot reactions to achieve a good overall yield of 50%, which is higher than that of making CF3-TCF. The reduced π–π stacking and fine-tuned bond-length alternation boost the nonlinear optical activities of FP-TCF-based heptamethines in plasmon-coupled EO polymer waveguides, leading to larger EO coefficients (up to 205%) over those of the TCF-based chromophores. More importantly, we demonstrate for the first time an ultralarge molecular first hyperpolarizability of 8437 × 10–30 esu at 1304 nm for M1a-FP-ON, which exceeds the results of two best-performing but synthetically demanding push–pull tetraene chromophores. The results mark an important milestone in developing highly efficient push–pull polymethines with good stability and synthetic scalability for photonic applications.

Poled polymers and their nonlinear optics

“…Luo et al synthesized dipolar heptamethines containing a strong electron acceptor, bis(4-fluorophenyl)-substituted TCF (FP-TCF), which has larger EO coefficients (up to 205%) than TCF-based chromophores. 40 It is attributed to the reduced p-p stacking and fine-tuned bond-length alternation. The study of electrostatic potential surface (ESP) by DFT calculations indicates the existence of a complementary combination of negatively charged cyano groups in TCF and FP-TCF acceptors and positively charged C-H bonds in the bridge and donor structures, leading to the formation of abundant hydrogen bonds in three-dimensional supramolecular architectures.…”

Electro-optic crosslinkable chromophores with ultrahigh electro-optic coefficients and long-term stability

“…Or adopt a more simplified chromophore synthesis scheme, such as the three-step synthesis method reported in the literature. 18 On the other hand, the glass transition temperature of the material also needs to be improved, preferably more than…”

“…Another solution is to adopt a more simplified chromophore synthesis scheme, such as the three-step synthesis method reported in the literature. 18 On the other hand, the glass transition temperature of the material also needs to be improved, preferably to more than 200 °C. Proper introduction of a small amount of polymer could help to increase the glass transition temperature without significantly reducing the chromophore content.…”

“…How to obtain organic electro-optic chromophores with a large electro-optic coefficient (r 33 value), photothermal stability and polarization orientation stability is still a problem to be solved. 18,19 In order to show the electro-optic activity, the chromophore molecules need to be polarized under the electric eld and exhibit a noncentrosymmetric arrangement. However, the chromophore molecules usually have large dipole moments, and the electrostatic interaction between the molecules will hinder the ordered arrangement, thus reducing the macroscopic electro-optic coef-cient.…”

Systematic Study on Nonlinear Optical Chromophores with Improved Electro-Optic Activity by Introducing 3,5-Bis(trifluoromethyl)benzene Derivative Isolation Groups into the Bridge

“…Different kinds of donors, acceptors, and bridges have been extensively studied to enrich the understanding of essential structure-nonlinear optical property and thermal stability correlations [ 26 , 27 , 28 , 29 ]. The introduction of some isolation groups (IG) into the chromophore moieties should be an efficient approach to decrease the interactions between chromophores and to enhance the nonlinear optical properties and the poling efficiency of organic electro-optic polymer materials [ 30 , 31 , 32 ]. These chromophores improve the application of nonlinear small molecules in the field of optical limiting and all-optical switching [ 33 ].…”